For application in lithium batteries, dye-sensitized solar cells, organic solar cells it is important to develop a non-corrosive, low cost, high level conductivity, and efficient electrolyte.
For example, the electrolyte that is currently used in DSSC solar cell is classed as poisonous, dangerous and corrosive. The high level of corrosive activity of electrolyte does not allow replacement of the Ti foil with another material. Development of new electrolyte could provide the possibility to utilize low cost materials for the anode substrate instead of Ti-foil. For example, it may be possible to replace Ti foil with Al foil.
Optimization DSSC, organic solar cells and Li-batteries request decreasing the internal resistance. For this goal the optimization of the properties of electrolyte is very important. Electrolytes must have high level of conductivity, chemical and electrochemical stability and high reliability over a long period within a wide range of operating temperatures. In the cased of DSSC and organic solar cells electrolyte must have a good transparency
For the purpose of thin film lithium batteries, DSSC and organic solar cell characteristic optimization and increasing serviceability it is important in particular, elimination of electrolyte leakage, using solid polymer electrolyte.
In the case of lithium batteries it must be solvent free polymer electrolyte with wide operation range of the potentials for the electrochemical stability.
In the case of the DSSC it must be red/ox active solid phase polymer electrolyte.
The Red/Ox couple in the electrolyte is of crucial importance for stable operation of a DSSC, because it must carry the charge between the photoelectrode and the counter-electrode for regeneration of the dye. After electron injection, the electron donor in the electrolyte must reduce the oxidized dye to the ground state as rapidly as possible. Thus, the choice of this charge mediator should take into account its redox potential, which must be suitable for regeneration the dye. Also, the redox couple must be fully reversible and should not exhibit significant absorption in visible light. Another important requirement is related to the solvent, which should permit the rapid diffusion of the dye from the oxide surface.
Polymer electrolytes may be the best option for this purpose. The poly(ethylene oxide) (PEO)-based solid polymer electrolytes have many potential applications in solid-state lithium batteries, dye-sensitized solar cells and organic solar cells.
The ionic conductivity of polymer electrolytes and their interfacial contact with electrodes are increased markedly by:                development of polymer electrolytes based high-molecular poly(ethylene oxide) (PEO with Mw=1,000,000) modified (plasticized) by oligomer propylene oxide derivatives (with Mw=725);        optimization of the terminal groups of propylene oxide and ethylene oxide derivatives (Mw=400-500) using them in oligomeric electrolytes;        development of electrolytes based on low-molecular weight poly(ethylene glycol) (Mw=1,000) with [2-(6-isocyanatohexyleaminocarbonylamino)-6-methyl-4[1H]pyrimidinone] providing quadruple hydrogen bond sites;        development of composite polymer electrolyte comprising PEO/DME, fumed silica, iodide salt and iodine.        
Nevertheless, it is necessary to note, that the developed electrolytes have not high enough conductivity, which at room temperature makes is 9.34*10−5 S·cm−1, 2.57*10−5 S·cm−1, 5.28*10−5 S·cm−1, accordingly, for the above electrolyte systems.
All the above electrolytes have essential disadvantage because of the presence of PEO (poly(ethylene oxide) or PPO (poly(propylene oxide) in their composition. It is known that PEO is characterized by a low glass transition temperature (Tg=−50° C.), but a regular structure favors a high degree of crystallinity (˜80%), with a melting point at Tf=65° C.
To obtain amorphous materials at ambient temperature, it is necessary to introduce some “disorder” in the structure of polymer matrix. This is achieved by cross-links in the network using co-polymers of PEO (for example, co-polymers of polyepichlorohidrins), or by incorporating into polymer matrix of silica or other oxides.
Under operation conditions, the problem of polymer electrolyte crystallization can effect significantly on long stable work of the device on its basis. There may also be a decrease in the performance efficiency of dye-sensitized solar cells in the field at low temperatures because of probable reduction of conductivity from such electrolytes.
Crystallization of PEO sharply reduces mobility of their segments and decreases a conductivity of a polymer matrix. That is why numerous efforts were done to find the ways to enhance an ionic conductivity of the PEO-containing electrolytes and simultaneously to lower or even to prevent the crystallization phenomenon. For this purpose the following operations were carried out:                For the lithium batteries the alkali metal salts with the large volume of anion (ClO4−, BF4−, PF6−, N(SO2CF3)2−, N(SO2CF2CF3)2− and others) were introduced in the content of polymer electrolytes.        Terminal groups on the PEO chains were modified.        PEO chains were included in the content of block and graft copolymers together with amorphous components such as poly(propylene oxide), polystyrene, poly(alkyl(meth)acrylates), due to this above copolymers are also used as matrices in the hard electrolytes.        
In the case of the linear block copolymers the largest decrease in the crystallinity degree, Xcr, was observed in the triblock copolymers with PEO central block and two side amorphous blocks. When the length of side blocks became higher than some critical value, depending on their chemical nature and PEO length, the triblock copolymer fully lost its ability to crystallize. In the graft copolymers, containing PEO grafts, the value of Xcr decreased the larger the less the length and quantity (density) of grafted chains. The relationship between Xcr and the parameters pointed was reverse for the graft copolymers with the main chain of PEO.
There is also once more way for a production of hard polymer electrolytes with practically full suppression of PEO crystallization, namely application as matrices the intermolecular polycomplexes (InterPC) of PEO with polyacids and other proton-donor polymers, which ones form due to hydrogen bonds. Indeed, the amorphous bulk structure of such InterPCs and their high binding ability with respect to ions, organic substances and colloid particles is well known. At the same time, their main drawback such as possibility to disintegrate to separate components under the effect of external stimuli (for example, of the temperature) or strong competitors (the solvent molecules, ions and other additives), which are capable to destruct the H-bond system, is also well known. This one can negatively influence on the formation of multicomponent polymer electrolytes, based on InterPC, of a solution and their following exploitation.
Taking into account the need to improve DSSCs and lithium batteries efficiency, it seems to us that for creation of polymer electrolytes, it is reasonable to use principally new approaches and materials providing high conductivity and stable operation over a wide temperature range.